While there are more than a few exceptions to the rule, most graffiti is nothing more but lame, self-serving tagging. But combine simple signatures with LEDs and slow shutter photography, and the genre is born anew:

Halo is a concept by French designer Aissa Logerot. Shaped like a bottle of spray paint, the LED light can change colors on the fly and while it's powered by an internal battery (that recharges with a simple shake of the can—a cutesy but awesome idea).

Combine this LED light with slow-shutter photography and you can freeze light graffiti in thin air without ruining a facade in the process. Of course, that non-destructive practicality probably eliminates any incentive for about 99.9% of graffiti enthusiasts.
[Halo via Core77]